Links for 2019-02-02

  • Understanding the bin, sbin, usr/bin , usr/sbin split

    omg. /usr/bin came about because Ken Thompson and Dennis Ritchie ran out of disk space on the root volume. Mind = blown

    You know how Ken Thompson and Dennis Ritchie created Unix on a PDP-7 in 1969? Well around 1971 they upgraded to a PDP-11 with a pair of RK05 disk packs (1.5 megabytes each) for storage. When the operating system grew too big to fit on the first RK05 disk pack (their root filesystem) they let it leak into the second one, which is where all the user home directories lived (which is why the mount was called /usr). They replicated all the OS directories under there (/bin, /sbin, /lib, /tmp…) and wrote files to those new directories because their original disk was out of space. When they got a third disk, they mounted it on /home and relocated all the user directories to there so the OS could consume all the space on both disks and grow to THREE WHOLE MEGABYTES (ooooh!).

    (tags: filesystem unix history ken-thompson dennis-ritchie disk-space usr)

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  1. Nix
    Posted February 4, 2019 at 01:19 | Permalink

    Decades of this split (and even now, with a ‘unified’ installation, it’s still done by having /usr in virtually everything and most things being symlinks into it) and it came about because they needed a new disk pack on one single installation.

    The only madder piece of ancient history in this area is the fact that the precedence of && and || is arguably wrong in C because back in truly ancient days there was only & and | doing double-duty, and when they split && and || off, they couldn’t give it a different precedence because the prospect of changing all that code in perhaps as many as ten whole C installations was far too much to contemplate.

  2. Justin Mason
    Posted February 4, 2019 at 12:43 | Permalink

    lol, fantastic :)